This application contains subject matter that may be related to that contained in the following U.S. applications filed on Feb. 19, 2002 and assigned to the assignee of the instant application: xe2x80x9cA Method and System for Monitoring and Profiling an Integrated Circuit Die Temperaturexe2x80x9d (Ser. No. 10/079,476), xe2x80x9cAn Integrated Temperature Sensorxe2x80x9d (Ser. No. 10/080,037), xe2x80x9cA Controller for Monitoring Temperaturexe2x80x9d (Ser. No. 10/079,475), xe2x80x9cTemperature Calibration Using On-Chip Electrical Fusesxe2x80x9d (Ser. No. 10/078,760), xe2x80x9cLow Voltage Temperature-Independent and Temperature-Dependent Voltage Generatorxe2x80x9d (U.S. Pat. No. 6,605,988), and xe2x80x9cIncreasing Supply Noise Rejection Using Voltage Regulators in an On-Chip Temperature Sensorxe2x80x9d (Ser. No. 10/078,130).
As shown in FIG. 1, monolithic integrated circuits (10) are fabricated several at a time on single chips (or xe2x80x9cwafersxe2x80x9d) (12) of silicon or dice (the singular being xe2x80x9cdiexe2x80x9d). This means that the passive and active structures of the integrated circuits (10) are manufactured all at the same time, thus ensuring that a large number of structures are identical, or bear some fixed ratio to one another. However, it is difficult to ensure that the electrical characteristics among the integrated circuits (10) are precisely the same. Thus, in effect, two integrated circuits (10) fabricated next to one another may have slightly different electrical characteristics. Such phenomena are known as process, or manufacturing, variations.
One particular variation that a chip designer has to compensate for involves those process variations that affect temperature measurements of an integrated circuit. It is becoming increasingly important to know the temperature parameters within which a particular integrated circuit operates because increased operating temperatures create a propensity for performance reliability degradation.
Because temperature considerations play a large part in the chip design process, it is imperative that a chip designer be able to make accurate temperature measurements of an integrated circuit. FIG. 2 shows a typical technique used to measure temperatures involving the use of a temperature-dependent voltage (Vprop in FIG. 2) to alter the frequency of a voltage controlled oscillator. A temperature-sensitive transistor (16) is disposed on a microprocessor (14) in order to measure temperature at a point on the microprocessor (14). The temperature-sensitive transistor (16) generates a temperature-dependent voltage (18) whose voltage is proportional to the temperature at the point at which the voltage generator (16) resides. The temperature-sensitive transistor (18) is used to control a voltage-controlled oscillator (VCO) (20), which acts as a voltage-to-frequency converter. The voltage-controlled oscillator (20) converts the temperature-dependent voltage (18) to an oscillating analog frequency (22) that is driven off of the microprocessor (14) to an off-chip measuring device (24).
This technique is prone to inaccuracy because the voltage-controlled oscillator (20) itself is susceptible to process variations. As a result, the oscillating analog frequency (22) generated by the voltage-controlled oscillator (20) may be an inaccurate representation of the voltage that is proportional to temperature (Vprop). In addition, digital circuitry of the microprocessor (14) cannot take advantage of Vprop represented by the oscillating analog frequency (22) because the oscillating analog frequency (22) is not converted from an analog quantity to a digital quantity, i.e., quantified, on the microprocessor (14). Thus, there is a need for a method of canceling process variations from the oscillating analog frequency (22), and a need for a method of quantifying Vprop on the microprocessor (14).
According to one aspect of the present invention, an apparatus for quantifying a difference in voltage between a temperature-independent voltage and a temperature-dependent voltage generated by a voltage generator comprises a first oscillator that inputs the temperature-independent voltage, where the first oscillator generates a first oscillating frequency based on the temperature-dependent voltage; a second oscillator that inputs the temperature-dependent voltage, where the second oscillator generates a second oscillating frequency based on the temperature-dependent voltage; and a comparator that compares the first oscillating frequency and the second oscillating frequency and generates a digital word representative of a difference between the first oscillating frequency and the second oscillating frequency.
According to another aspect, an apparatus for quantifying a difference in voltage between a first nodal voltage and a second nodal voltage generated by a voltage generator comprises means for generating a first oscillating frequency based on the first nodal voltage; means for generating a second oscillating frequency based on the second nodal voltage; and means for generating a digital word representative of a comparison of the first and second oscillating frequencies.
According to another aspect, a method for quantifying a difference in voltage between a first nodal voltage and a second nodal voltage generated by a voltage generator comprises generating a first oscillating frequency based on the first nodal voltage, where the first oscillating frequency is generated with a first oscillator; generating a second oscillating frequency based on the second nodal voltage, where the second oscillating frequency is generated with a second oscillator; and generating a digital word in relation to the first and second oscillating frequencies, where the digital word is generated with a comparator.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.